This invention relates to improved structure for adjusting the position of clutch members to compensate for wear.
Clutches are known wherein leaves selectively force drive and driven discs into contact to transmit drive from a flywheel to a driven shaft. A flywheel housing rotates with the flywheel, and an adjusting ring attached to the flywheel housing provides an abutment face to properly position the levers relative to the other members of the clutch. The adjusting ring is threadably adjustable relative to the flywheel housing to vary the position of the levers, and compensate for wear on the drive and driven discs. The prior art has typically used adjustment threads which extend continuously around the entire inner peripheral surface of the flywheel housing, and the entire outer peripheral surface of the adjusting ring. Further, the prior art threads have typically had a relatively small lead such that there has been a relatively great number of thread turns per unit of axial length. As an example, in one prior art clutch there are eleven thread turns per inch of length. Also, the prior art has typically used standard bolt threads which have a cross-section with a sharp extending portion at one lateral end of the thread.
The adjustment threads used with such a prior art clutch have several drawbacks. The adjustment threads are typically exposed to impurities, debris and moisture such that the thread surfaces between the adjusting ring and the flywheel housing may bind or rust. As the adjusting ring is adjusted, debris which may be on the continuous adjustment threads is trapped and can become embedded into spaces between the adjustment threads on the adjusting ring and the flywheel housing. Further, with the prior art adjustment threads it is difficult to maintain a sufficient amount of lubricant between the adjustment threads on the flywheel housing and the adjusting ring. A leading edge of the sharp extending portion of the prior art thread will sometimes scrape away the lubricant as the adjusting ring turns relative to the flywheel housing. The lack of lubricant may allow the members to rust. Eventually, the adjusting ring and the flywheel housing may lock up and no longer be adjustable.
There are known clutches having channels cut into the adjusting ring which form gaps in the adjustment thread. The channels are formed to allow passage of various clutch members, and are relatively deep. Due to their depth, the channels may capture and remove too much lubricant, and result in the adjustment threads on the adjusting ring and flywheel housing having insufficient lubricant, and rusting.